I agree that "either" is more specific. And I don't mind being reminded of it.
Otoh "any" is defined as ∃ x and every definition I found explicitely specified that cardinality is irrelevant. Either then is a subset of any, not a separate category.
So imho this isn't a mistake and you're way more unconditional than you should.
PS: as long that everyone remains sufficiently mutually understandable we should adopt a descriptivist attitude towards languages instead of a prescriptivist one.
PPS: Don't get me started on language as a class marker. This is a threat. c:
Pretty much every damn thing is political.
"it's just politics" is such an empty statement.